1. Field of the Invention
The present invention relates generally to liquid crystal display devices and, more particularly, to liquid crystal display devices of the thin-film transistor type with test procedures made easier for inspection of functional operabilities of thin-film transistors and connection failures at scan line lead lines and/or signal line leads. This invention also relates to a method for manufacturing the same.
2. Description of the Related Art
Liquid crystal display devices are widely employed as high-precision color display devices for use in notebook computers and display monitor units.
Currently available liquid crystal display devices include those of the simple matrix type using a liquid crystal panel with a liquid crystal layer interposed between a pair of substrate having inside surfaces on which parallel electrodes are formed in a manner that these cross over each other, and the ones of the active matrix type using a liquid crystal display element (referred to also as liquid crystal panel hereinafter) having switching elements for selection in units of pixels on one of a pair of substrates.
Active-matrix liquid crystal display devices include a liquid crystal display device of the so-called longitudinal electric field scheme such as twisted nematic (TN) scheme (generally called TN type active-matrix liquid crystal display device) using a liquid crystal panel with a group of pixel selection electrodes formed on a respective one of a pair of upper and lower substrates, and a liquid crystal display device of the so-called lateral electric field scheme (generally known as IPS type liquid crystal display device) using a liquid crystal panel with such pixel selection electrode group formed on only one of a pair of upper and lower substrates.
Typically a liquid crystal panel making up the former Tn type active-matrix liquid crystal display device is such that liquid crystals are aligned to twist by 90xc2x0 within an interior space of a pair of substrates (two substrates consisting of a first substrate (lower substrate) and second substrate (upper substrate)), wherein two polarization plates are multilayered on outside surfaces of the upper and lower substrates of such liquid crystal panel respectively, with absorption axis directions being disposed in a cross polarization or xe2x80x9ccrossed Nicolxe2x80x9d fashion and also with light entrance side absorption axes being in parallel or at right angles to a rubbing direction.
In the TN type active-matrix liquid crystal display device thus arranged, incident light becomes linearly polarized light at an incidence side polarization plate upon application of no voltages. This linear polarized light travels along twisting of a liquid crystal layer and if the penetration axis of a light output side polarization plate is identical to the azimuth angle of the linear polarized light then all rays of the linear polarized light are permitted to go outwardly resulting in establishment of a white display (what is called the xe2x80x9cnormally open modexe2x80x9d).
In voltage application events a unit vector""s direction (director) indicating the average orientation direction of axes of liquid crystal molecules constituting the liquid crystal layer becomes perpendicular to substrate surfaces while the azimuth angle of incidence side linear polarized light is kept unchanged, thus resulting in coincidence with the absorption axis of the light output side polarization plate to thereby obtain a black display (see xe2x80x9cBasics and Applications of Liquid Crystals,xe2x80x9d issued by Industry Research Association. 1991).
On the other hand, in an IPS type liquid crystal display device with pixel selection electrodes and electrode leads formed on only one of a pair of substrates for permitting switching of its liquid crystal layer in a specified direction extending in parallel to substrate surfaces through voltage application between neighboring electrodes (between a pixel electrode and counter electrode) on this substrate, polarization plates are so disposed as to to provide the black display when no voltages are applied thereto (so called the xe2x80x9cnormally close modexe2x80x9d).
The IPS type liquid crystal display device""s liquid crystal layer exhibits homogeneous alignment or orientation parallel to the substrate surfaces in the initial state. Simultaneously the director of the liquid crystal layer in a plane parallel to the substrates is parallel or slightly angled to the electrode lead direction upon application of no voltages, causing the direction of the director of the liquid crystal layer in voltage application events to shift toward a direction perpendicular to the electrode lead direction upon application of a voltage thereto. When the liquid crystal layer""s director direction is tilted toward the electrode lead direction by 450xc2x0 in comparison with the director direction when no voltage are applied thereto, the liquid crystal layer upon application of the voltage causes the azimuth angle of polarized light to rotate 90xc2x0 as in {fraction (1/2)} wavelength plates resulting in coincidence between the light output side polarization plate""s transmission axis and the polarized light""s azimuth angle thus providing a white display.
This IPS type liquid crystal display device has its feature that changes in color phase and contrast stay less even at viewing angles thus enabling achievement of wide view-field angles (see Japanese Patent Laid-Open No. 505247/1993).
A major approach to attain full color image visualization of the respective types of liquid crystal display devices stated supra is to employ a color filter scheme. This is for realization by subdividing a pixel corresponding to a single dot of color display into three portions and disposing color filters of the three primary colorxe2x80x94e.g. red (R), green (G), and blue (B)xe2x80x94at such unit pixels respectively.
Although the present invention is applicable to the several types of liquid crystal display devices stated above, its outline will be explained below with a TN type active-matrix liquid crystal display device being as an example.
As previously stated, in a liquid crystal element (liquid crystal panel) making up the TN type active-matrix liquid crystal display device (referred to simply as active-matrix liquid crystal display device hereinafter for brevity purposes), there are formed on a liquid crystal layer side surface of one substrate of two transparent dielectric substrates typically made of glass plates mutually opposed with a liquid crystal layer interposed therebetween a group of scanning signal lines (referred to as gate lines hereinafter) extending in its xe2x80x9cxxe2x80x9d direction and being parallel disposed in xe2x80x9cyxe2x80x9d direction and a group of drain lines (video signal lines) isolated from this gate line group and extending in the y direction while being parallel disposed in the x direction.
A respective one of regions surrounded by these gate line group and drain line group becomes a pixel region in which a thin-film transistor (TFT) for use as an active element (switching element) and a transparent pixel electrode are formed by way of example.
When a scan signal is supplied to a gate line, the thin-film transistor turns on causing a video signal coming from a drain line to be supplied to the pixel electrode via this turned-on thin-film transistor.
Additionally each drain line of the drain line group and each gate line of the gate line group are extended up to the periphery of a substrate to constitute external terminals respectively, to which video drive circuits and gate scan drive circuitsxe2x80x94namely a plurality of drive IC chips (semiconductor integrated circuits as will be referred to simply as drive ICs or ICs hereinafter) making up these circuitsxe2x80x94are connected respectively, which are separately mounted at the substrate periphery. In other words a plurality of tape carrier packages (TCPs) with these respective drive ICs mounted thereon are externally bonded to peripheral portions of the substrate.
However, since such substrate is designed so that TCPs with drive ICs mounted are externally attached at the peripheral portions thereof, the occupation area of a region (generally called xe2x80x9cpicture framexe2x80x9d) defined between contour lines of a display region as formed of the substrate""s cross-over regions of the gate line group and drain line group and an outer frame of the substrate becomes larger undesirably, which is against a demand for reducing or minimizing the outside dimensions of a liquid crystal display module with the liquid crystal display element and an illuminance light source (backlight unit) and other associative optical elements integrated therein together.
Thus, in order to avoid this problem or at least minimize risks, i.e. to fully meet demands for high-density mountability of the liquid crystal display element and also downsizing of the outer size of liquid crystal display module, the so-called flip-chip scheme or alternatively chip-on glass (COG) scheme has been proposed for permitting direct mounting of drive ICs for video driving and drive ICs for scan driving on one substrate (lower substrate) without the use of any TCP components. And, the drive ICs are designed to employ the so-called FCA scheme for permitting electrodes formed on back surfaces of such drive ICs to be directly connected to electrical wiring leads formed on the substrate.
FIG. 10 is a perspective view diagram for explanation of main part of a liquid crystal display device of the FCA mount scheme. This liquid crystal display device is arranged so that a liquid crystal layer is interposed between one substrate SUB1 with a matrix array of thin-film transistors formed thereon and a remaining substrate SUB2 with color filters formed thereon.
The one substrate SUB1 has its one peripheral side along which scan line drive ICs (referred to as gate drivers hereafter) GDR are mounted by the FCA scheme. In addition signal line drive circuit ICs (drain drivers) DDR are similarly mounted by FCA scheme along another side of the substrate.
Outputs of the gate drivers GDR are connected to scan line extension leads GTM whereas inputs thereof are connected to wiring lines of a flexible printed circuit board FPC1. Outputs of the drain drivers DDR are connected to signal line leads DTM; their inputs are coupled to wiring lines of a flexible printed circuit board FPC2.
As shown by arrows In FIG. 10, the flexible printed circuit boards FPC1, FPC2 are such that the flexible printed circuit board FPC1 is bent in a direction BENT1 toward the back surface of one substrate SUB1; then, a curvature portion JT2 of the flexible printed circuit board FPC2 is folded along a fold line BTL in the BENT1 direction and then folded in a direction BENT3 for accordion-like folding onto the back surface of flexible printed circuit board FPC1.
Under this condition, let the flexible printed circuit board FPC2""s connector CT4 be connected to a connector, not shown, as provided on the flexible printed circuit board FPC1. An adhesive tape BAT is interposed on the inner surface of the folded portion of the flexible printed circuit board FPC2, resulting in fixture to flexible printed circuit board FPC2.
Note here that reference characters xe2x80x9cCHGxe2x80x9d and xe2x80x9cCHDxe2x80x9d designate electronics components such as capacitors and others; ALMG, ALMD denote alignment marks; POL2 is a polarization plate; AR, a display region.
In the liquid crystal display device with the above arrangement, let probes of test/inspection equipment be attached to extension leads of the gate lines and extension leads of the drain lines which are extended from the thin-film transistors formed on one substrate SUB1 to thereby perform several tests for inspection of thin-film transistor characteristics and connection failures at respective electrical leads and turn-on or xe2x80x9clightingxe2x80x9d tests after adhesion with the other substrate.
FIG. 11 is a layout explanation diagram of test terminals in one prior art liquid crystal display device, wherein part (a) is a pictorial representation of the gate driver side whereas (b) depicts the drain driver side.
At the part (a), GTM designates gate line extension leads; TPC denotes test terminals; GDR indicates gate driver mount portions (shown by dot lines); LCT is a laser cut line; ASCL, a gate line side static electricity suppression common line; GTM, input terminals of the gate drivers GDR.
In the manufacture of one substrate SUB1 (thin-film transistor substrate), the gate line extension leads GTM are short-circuited by the static electricity suppression common line ASCL for protection against damages of thin-film transistors and wiring leads occurring due to invasion of static electricity. Thereafter, individually cut the gate line leads GTM along the laser cut line LCT; then, attach the probes to the test terminals TPC for inspection of connection failure or unwanted open-circuiting while performing lighting tests upon application of more than one signal thereto.
In part (b), DTM designates drain line extension lines; TPC denotes test terminals; DDR indicates drain driver mount portions (shown by dot lines); LCT is a laser cut line; ASCL, drain line side static electricity suppression common line; TTB, input terminals of the gate drivers GDR.
Similarly, on the drain driver side also, in the manufacture of such substrate, the drain line extension leads DTM are short-circuited by the static electricity suppression common line ASCL for preclusion of damages due to invasion of static electricity at thin-film transistors and wiring leads concerned. Thereafter, individually cut the drain line leads DTM along the laser cut line LCT: then, attach all the probes to the test terminals TPC at a time for open-circuit inspection while performing lighting tests upon application of a signal(s) thereto.
An example of this flip-chip scheme liquid crystal display device is disclosed in Japanese Patent Laid-Open No. 122806/1996.
In the prior art test terminal layout, the requisite number of gate drivers and drain driversxe2x80x94in particular drain driversxe2x80x94increases with growth in high-precision displayability, resulting in a decrease in pitch of output terminals thereof (pitches of GTM and DTM of FIG. 11).
As a result, it becomes impossible to provide sufficiently large widths and lengths of the test terminals (TPC of FIG. 11), which in turn makes it difficult to achieve simultaneous contacting of all probes as in the prior art, leading to occurrence of a problem as to a decrease in inspection accuracy due to probe deviation during open-circuit and lighting tests while externally applying test voltages to the test terminals involved. In addition, production of such probes applied to the output terminals with such narrow pitches is also becoming more difficult.
An object of the present invention is to avoid the problems faced with the prior art to thereby provide a liquid crystal display device having a wiring lead structure capable of execution of a variety of kinds of tests with simultaneous contact of probes to all terminals at a time and also capable of using test/inspection apparatus having probes with common useabilities for multiple types of products by standardization of a pattern of test terminals.
Another object of this invention is to provide a liquid crystal display device capable of facilitating production of the probes at low costs and a method for manufacturing the device.
A further object of the invention is to provide a liquid crystal display device similar to that stated above and capable of suppressing reduction of detection abilities as to display defects during inspection and a manufacturing method thereof.
To attain the foregoing objects the present invention provides as its representative means a technique for subdividing output terminals (lead lines) of drain drivers into six separate groups with regard to the three primary colors of red, green and blue, which groups are of a positive polarity of red, negative polarity of red. positive polarity of green, negative polarity of green, positive polarity of blue, and negative polarity of blue, wherein respective ones are bundled and connected together to drain line common lines, which are taken out of a drain driver mount region for permitting execution of inspection while letting probes be attached to test terminals as provided at the drain line common lines.
In addition, regarding the gate driver side, a technique is provided as a representative means for classifying output terminals (lead lines) of gate drivers into three groups of a front stage, next stage and rear stage or alternatively four groups for letting polarities become reversed in units of respective dots, wherein respective ones are bundled and connected together to gate line common lines, which are taken out of a gate driver mount region for permitting execution of inspection while letting probes be attached to test terminals as provided at the gate line common lines.
Some representative arrangements of the present invention will be set forth below.
(1) In a liquid crystal display device including:
a pair of substrates with a liquid crystal layer interposed therebetween, one of said substrates having thereon a matrix array of thin-film transistors, pixel electrodes as driven by the thin-film transistors, and a pattern of scanning lines and signal lines for supplying the thin-film transistors with voltage signals used for pixel formation, a remaining one of said substrates having color filters of three colors of red and green plus blue, the one substrate also having a peripheral si de with scan line lead terminals provided and another peripheral side with signal line lead terminals provided;
a scan line drive IC mount region and signal line drive IC mount region having output terminals connected to respective ones of said scan line lead terminals and said signal line lead terminals of the liquid crystal panel while permitting direct mount of more than one scan line drive IC and more than one signal drive IC respectively: and
more than one static electricity suppression common line provided in a cut removal region for commonly connecting said scan line lead terminals and signal line lead terminals together,
the device is specifically arranged to comprises:
six signal line side common lines provided in the signal line drive IC mount region of the signal line lead terminals connected to said static electricity suppression common line, for connection with six terminal groups as divided from the signal line lead terminals in a way such that the groups are of positive polarity of red, negative polarity of red, positive polarity of green, negative polarity of green, positive polarity of blue, and negative polarity of blue; and
test pads provided on said one substrate in an area excluding said signal line drive IC mount region for connection to said six signal line side common lines.
With such an arrangement, it is possible to enlarge the width and length plus pitch of test pads for connection to the signal line leads, thus making it possible to make easier production of the probes, resulting in an increase in contact accuracies.
(2) The test pads of said six signal line side common lines are disposed in the cut removal region of said one substrate.
It is possible to standardize patterns of the test pads, thereby enabling the intended inspection of liquid crystal display devices of multiple types of products to be done by use of test apparatus or equipment having a common probe or probes.
(3) In a liquid crystal display device including:
a pair of substrates with a liquid crystal layer interposed therebetween, one of said substrates having thereon a matrix array of thin-film transistors, pixel electrodes as driven by the thin-film transistors, and a pattern of scanning lines and signal lines for supplying the thin-film transistors with voltage signals used for pixel formation, a remaining one of said substrates having color filters of three colors of red and green plus blue, the one substrate also having a peripheral side with scan line lead terminals provided and another peripheral side with signal line lead terminals provided;
a scan line drive IC mount region and signal line drive IC mount region having output terminals connected to respective ones of said scan line lead terminals and said signal line lead terminals of the liquid crystal panel while permitting direct mount of more than one scan line drive IC and more than one signal drive IC respectively; and
more than one static electricity suppression common line provided in a cut removal region for commonly connecting said scan line lead terminals and signal line lead terminals together,
the device comprises: three scan line side common lines provided in the scan line drive IC mount region of the scan line lead terminals as connected to the static electricity suppression common line, for connection with three groups being divided from the scan signal line lead terminals and having a front stage and next stage plus rear stage or alternatively four terminal groups as divided therefrom in order to let the polarity become reversed in units of dots;
six signal line side common lines provided in the signal line drive IC mount region of the signal line lead terminals connected to said static electricity suppression common line, for connection with six terminal groups as divided from the signal line lead terminals in a way such that the groups are of positive polarity of red, negative polarity of red, positive polarity of green, negative polarity of green, positive polarity of blue, and negative polarity of blue; and
test pads provided on said one substrate in an area excluding said scan line drive IC mount region and said signal line drive IC mount region for being associated with said three or four scan line side common lines and said six signal line side common lines respectively.
With this arrangement, it is possible to enlarge the width and length plus pitch of test pads for connection to the signal line leads, thus making it possible to make easier production of the probes, resulting in an increase in contact accuracies.
(4) The test pads of said three or four scan line side common lines and said six signal line side common lines are disposed in the cut removal region of said one substrate.
(5) The test pads of said three or four scan line side common lines and said six signal line side common lines are laid out with equal intervals in the cut removal region of said one substrate.
It is possible to standardize patterns of the test pads including scan lead lines also, thereby enabling the intended inspection of liquid crystal display devices of multiple types of products to be done by use of test apparatus or equipment having a common probe or probes.
(6) Said remaining substrate has thereon more than one counter electrode, the test pads of said three or four scan line side common lines and said six signal line side common lines are disposed in the cut removal region of said one substrate, and a test pad for connection to a lead line of the counter electrode is disposed along with the test pads of said three or four scan line side common lines and said six signal line side common lines.
It is possible to further promote standardization of patterns of the test pads including scan lead lines also, thereby enabling the intended test of liquid crystal display devices of multiple types of products to be done by use of test apparatus or equipment having a common probe or probes.
(7) Said one substrate has thereon more than one counter electrode, the test pads of said three or four scan line side common lines and said six signal line side common lines are disposed in the cut removal region of said one substrate, and a test pad for connection to a lead line of the counter electrode is disposed along with the test pads of said three or four scan line side common lines and said six signal line side common lines.
Since it is possible to dispose those lead lines of counter electrodes required for turn-on or xe2x80x9clightingxe2x80x9d tests also in the form of a standard pattern along with the test pads of the scan line side common lines and signal line side common lines, it becomes possible to further promote standardization of the test pad patterns, thereby enabling the intended test of liquid crystal display devices of multiple types of products to be done by use of test apparatus or equipment having a common probe or probes.
One significant feature of the present invention as disclosed and claimed herein lies in separation of the signal side common lines at least in units of respective colors of the color filters in the way stated previously. This invention is not the one that excludes arrangements for performing inspection while causing only the same signal to input to a video signal line concerning each color in any events. However, separating the signal side common lines at least in units of colors of the color filters as stated above makes it possible to reduce probe costs due to reduction of the requisite number of test pads to thereby enable achievement of tests with colors being displayed while at the same time enabling execution of the intended test procedure with high accuracies. In cases where the color filters are of the three primary colors of red, green, and blue, any kinds of tests become available with respect to almost every color to be displayed at products through individual inspections of red, green and blue due to lighting in units of respective colors in addition to white displaying with all colors being brightened at a time, and further lighting while controlling the gray-scale gradation levels of each color.
This means that color purity tests of respective colors become possible, which is a significant advantage of the arrangement incorporating the principles of the invention. Further, demonstrable improvement in test accuracies of display irregularities is realized, which is an effect that will no longer be attained by exclusive use of all-color simultaneous lighting schemes. The color filters are formed by a process having the steps of performing deposition and exposure plus development separately in units of colors thereof or alternatively by letting the individual colors be impregnated. Accordingly in-plane uniformity or distribution within a plane of film thickness will take place in units of respective colors. In the case of lighting all colors at once, influences of these will normally become inappreciable. For example, in case only the film thickness of red locally changes, the resultant influence of such red film thickness""s local change upon brightness or luminance during simultaneous lighting of all of the three colors of red, green and blue becomes ⅓ of that during uni-color lighting of red. Accordingly, the only use of all-color simultaneous lighting would result in occurrence of luminance irregularitiesxe2x80x94in. particular, a decrease in inspection sensitivities as to color irregularities, which leads to risks of outflow of defective products into the market. With the instant invention, it is possible by separating the signal side common lines at least in units of respective colors of the color filters in the way stated supra to establish tests with the colors being lit individually, which in turn makes it possible to realize probe cost reduction and test cost reduction plus high-precision product""s lighting tests while retaining test accuracies concerning luminance and color irregularities.
Although this test scheme is advantageous especially for FCA, similar results are also obtainable in TCP schemes through separation of the signal side common lines at least in units of colors of the color filters.
Another significant feature of the invention is that the signal side common lines are separated at least in units of colors of the color filters and for use as positive and negative polarities. Whereby, if the color filters are of three colors by way of example, then the resulting signal side common lines become six lines. Currently available liquid crystal display device drive methods include two major ones: a common inversion driving method, and dot inversion drive method. The common inversion drive is such that at least three signal line side common lines are employed as discussed above due to the fact that in most cases the pixels neighboring in a scan signal line extension direction are the same as each other in polarity relative to the reference signal potential. On the contrary, the dot inversion drive method is such that neighboring pixels in the scan signal extension direction are ordinarily driven in such a way that these are of opposite polarities relative to the reference signal potential. Due to this, in the case of using three signal line side common lines in dot inversion events, six certain pixels neighboring in the scan line extension direction become xe2x80x9c+xe2x88x92++xe2x88x92+xe2x80x9d by way of examplexe2x80x94in this case, any intended polarity inversion is no longer realizable between B and R. Even in this case, the above-noted detection accuracies of luminance/color irregularities can be maintained almost perfectly. Regrettably this advantage does not come without accompanying a penalty which follows: it becomes difficult to accurately inspect flicker, i.e. on-screen flickering, to be checked during lighting test procedure. Generally this flicker will become problematic only with special patterns or only at special timings, which is less in influence during real in-use events than the above-noted color/luminance irregularities; however, if such flicker stays at levels greater than a level defined by clients then a product with the flicker must be regarded as a defective one. Accordingly, with the invention, separating the signal side common lines in units of colors of the color filters and for use as the positive and negative polarities, e.g. employing six signal side common lines for use with color filters of the three primary colors, makes it possible to cause an array of six pixels of RGBRGB to have reversed polarities between adjacent ones of them in a pattern of xe2x80x9c+xe2x88x92+xe2x88x92+xe2x88x92xe2x80x9d by way of example.
Further, the flicker inspection accuracy in particular is variable depending upon the influence of a very small voltage difference between pixels; thus, it is required to control any possible delays of signal waveforms during inspection. Thus it is desirable that an increased number of test pads for input of test signals to signal line side common lines be provided with respect to each signal line, which number is given as (nxe2x88x921)/2 or more where xe2x80x9cnxe2x80x9d is the number of pads per unit region, which may be a chip mount region or alternatively a region with an ensemble of signal wiring leads provided therein. In addition, to suppress probe cost increases, it is desirable that the pad number be set at 2xc3x97(n+1) or less.
It is also desirable that the number of test signal terminals for inputting test signals to scan signal lines is greater than the number of test signal terminals for input of test signals to video signal lines. This is based on a requirement for reducing input resistivities of the video signal line side while taking account of the fact that execution of the intended test/inspection with the above-noted arrangements requires that the input frequencies of certain test signals to be applied to the video signal lines during inspection be higher than or equal to input frequencies of test signals being applied to the scan signal lines.
In addition, advantages as to lower resistivities are obtainable by providing a region formed of a specific wiring layer with the lowest resistivity in the liquid crystal display device at any one of those wiring leads associated with the signal line side common lines or alternatively between the signal line side and test pads and leads associated with the scan line side common lines or between the scan line side common lines and test pads.
Furthermore, with the invention, the scan line side common lines are arranged by more than two lines. Use of a single line enables all-line simultaneous lighting. However, difficulties can occur in regard to the above-mentioned flicker lighting inspection. More specifically, for either one of the common inversion driving and dot inversion driving, drive is done in real in-use states in such a way that two neighboring pixels in an extension direction of video signal lines are reversed In polarity to each other. This is for the purpose of flicker suppression. Thus, in order to perform inspection as to flicker, it is required to drive in a way that two neighboring pixels in the video signal line extension direction are mutually reversed in polarity. As the use of a single scan line side common line must result in such two pixels being the same in polarity as each other, there is a problem that no flicker tests are achieved in real in-use states. In view of this, by employing two lines for permitting two neighboring pixels to be deviated or shifted in write timing, it becomes possible to drive in such a way that the two neighboring pixels in the video signal line extension direction to be mutually reversed in polarity, thus enabling the intended flicker test.
In addition, with regard to the flicker, the influence of a xe2x80x9cjump-inxe2x80x9d voltage upon writing into a TFT is also present. To let this be closer to a real-use state, it is desirable that more than three scan line side common lines be employed in specific liquid crystal display devices of the so-called Cadd scheme with a capacitor for storage of electrical charge as written into a pixel electrode being formed in particular between the pixel electrode and scan signal line at the rear stage. Since with this technique the front stage pixel""s Cadd is formed on a scan signal line at the self stage and, further, the self stage pixel""s Cadd is formed on a scan signal line at the rear stage, any intended writing into pixels in a way equivalent to real use events is realized by scanning a pixel at the self stage and its front and rear pixels in a specified order of sequence similar to that during real use states. Additionally, in certain schemes that do not constitute Cadd such as for example Cstg scheme or else, writing equivalent to real use events is possible even when the scan line side common lines consist of mere two lines; however, in regard to the influence of voltage potentials due to capacitive coupling between pixels, the use of more than three scan line side common lines in a similar manner exhibits an effect for approximation to real in-use states.
Note here that in the case of three lines, at six pixels ABCDEF aligned in a direction along the image signal line extension direction, the polarities of respective pixels relative to a reference signal potential become xe2x80x9c+xe2x88x92++xe2x88x92+xe2x80x9d by way of example, resulting in occurrence of a problem that pixels C and D, for example, are the same in polarity as each other. To avoid this problem, it will be desirable that the scan line side common lines consist of an even number of lines. In view of the problem in the Cadd scheme, it is deemed most effective to arrange them while employing four lines as a minimal number in the Cadd scheme or using two or four lines in the Cstg scheme.
The present invention should not be limited to the above stated arrangements or arrangements of embodiments to be set forth later in the description and ideas as disclosed therein. A variety of modifications and alterations will be possible without departing from the true spirit and scope of the invention.
Several preferred embodiments of the instant invention will now be explained in detail with reference to the accompanying drawings below. Although the following embodiments will be set forth in conjunction with liquid crystal display devices of the so-called TN type, the same goes with basic configurations of portions of devices of the IPS (lateral electric field) scheme to which the invention is applied except that counter electrode lead lines are drawn out on the thin-film transistor substrate side.
In addition, in the explanation presented below also, signal lines are also called drain lines whereas scan lines are called gate lines.